302 backfire
New User
Joined: Jun 2002
Posts: 22
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From: Shawnee
302 backfire
I've got a '87 F150 4x4 4 speed with granny ,302 EFI that farts while under acceleration. It's not a muffler backfire and a little more than a cough. It sounds like it may be muffled by the breather apparatus or it could be a valve popping somewhere. If I ease into it I can avoid the popping, and it does it the least while cold. Both fuel tanks have sending unit problems and it doesn’t run well under a load on the back tank. Sometimes the back tank works ok but mostly it runs out about a half a gallon of gas then starts starving. I wonder if these two problems are connected in any way? I have autolite plugs gapped about 42 and I separated the #7 and #8 plug wire. Had a broken exaust manifold so I had it in the garage and my mechanic checked and moved the timinng just a little to about 12. The truck has about 160k miles on it and the engine was overhauled by a reputal shop at 100k miles. The problem was there before the overhaul. Thanks for your help.
Senior User
Joined: Jan 2002
Posts: 185
Likes: 0
From: Central Florida, USA
302 backfire
Backfires, exhaust gasses traveling up through the intake manifold, are almost always caused by incorrect ignition timing. Could be your distributor timing or your cam timing. Ignition timing should be 10° BTDC with the advance disabled. You will have to pull the water pump and timing chain housing to see if your cam timing chains are worn or have jumped a notch.
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